Conventional air conditioners are normally operated or stopped when the indoor temperature that is detected by a temperature sensor provided in a suitable place in a room (for example, near the air conditioner) has reached a preset indoor temperature. Therefore, it is known that a loss of energy occurs even when the indoor temperature that is detected by the temperature sensor has reached the set indoor temperature because, if heating is continued, the temperature on or near the ceiling becomes higher than the set indoor temperature, and if cooling is continued, the temperature on or near the floor becomes lower than the set indoor temperature.
Therefore, in order to solve the above-described loss of energy, detecting a difference in the upper and lower temperatures in the room, and stirring the indoor air when the temperature difference exceeds a set value has been proposed (Japanese Patent Application Laid-Open (JP-A) No. 5-180459).
According to this known invention, since the temperature difference between the upper part and the lower part of the room is detected and a convection is generated in the room, the loss of energy in air conditioning caused by high-temperature air accumulating near the ceiling and low-temperature air accumulating in the vicinity of the floor can be improved. However, energy saving by using this process together with the conventional air conditioner has not been taken into consideration. Moreover controlling the power that is supplied to a fan for generating the convection in the room based on the size of the temperature difference between the upper part and the lower part of the room has also not been taken into consideration. Furthermore, controlling the feed rate of energy (for example, the quantity of power, gas, fuel oil or the like) to the air conditioner that is installed in the room has also not been taken into consideration.
When the indoor space is large (for example, in offices, stores, assembly halls, public office buildings, schools, hospitals, factories, greenhouses, etc.), it is necessary to provide a large number of air supply and exhaust openings so as to generate the convection in the indoor air. However, the opening and closing control of the large number of air supply and exhaust openings or the control of a flow rate at the time of supplying or exhausting the air has not been suggested at all.